This invention relates generally to vacuum heat treating furnaces, and in particular, to a nozzle for injecting a cooling gas into the hot zone of such a furnace.
Many of the known vacuum heat treating furnaces available hitherto, incorporate cooling gas injection systems to provide rapid cooling of metal parts from the elevated heat treatment temperature. Among the components of the cooling gas injection system used in such furnaces are a plurality of nozzles for conducting the cooling gas into the furnace hot zone. The gas injection nozzles used in the known systems are generally tubular or cylindrical in shape and have a central opening that extends along the length of the nozzle.
A problem arises when using such nozzles in a vacuum heat treating furnace because the known nozzles have unobstructed openings therethrough, and heat can be lost from the hot zone during the heating cycle. Heat loss occurs when the heated atmosphere in the furnace hot zone exits the hot zone through the cooling gas nozzles and is cooled in the plenum or, in a plenumless furnace, in the space between the hot zone and the furnace wall. The heated gas is cooled as it traverses the plenum or the annular space between the hot zone and the water-cooled furnace wall in a plenumless furnace and reenters the hot zone at a lower temperature. This problem occurs in vacuum furnaces that utilize convection heating, as well as those that utilize radiant heating of the metal work pieces.
Such heat loss results in a non-uniform heating of the metal parts. When the metal parts do not uniformly attain the desired heat treating temperature, the properties desired from the parts are not achievable.
Consequently, a need has arisen for a cooling gas injection nozzle which substantially prevents the heat in the hot zone from exiting the hot zone during a convection or other heating cycle. Some furnaces have incorporated mechanically actuated dampers or covers on the cooling nozzles. However, such devices are operated from outside the vacuum furnace and thus require complex mechanical linkage systems. It would be highly desirable to have a simple device for injecting cooling gas into a vacuum heat treating furnace which substantially inhibits the escape of heated gas therethrough.
The problems discussed above are resolved to a large degree by a cooling gas injection nozzle for a vacuum heat treating furnace in accordance with this invention. The gas injection nozzle according to the present invention includes a forward portion having a first central opening formed therethrough. The nozzle also has a rear portion with a second central opening formed therethrough. A flap is disposed in and pivotably supported in the first central opening. This flap operates to substantially prevent the escape of heated atmosphere from the hot zone during a heating cycle, but to permit the injection of a cooling gas into the furnace hot zone during a cooling cycle. The nozzle according to the present invention is supported from the hot zone wall by any appropriate means.
In accordance with another aspect of the present invention there is provided a vacuum heat treating furnace having a vacuum vessel, a hot zone disposed in said vacuum vessel, and a plurality of cooling gas injection nozzles as described above which are disposed in said hot zone. In accordance with a further aspect of the present invention, there is provided a hot zone for a vacuum heat treating furnace that includes a closed wall defining an internal volume, insulation disposed over an interior surface of the closed wall, and a plurality of cooling gas injection nozzles as described above disposed in the hot zone.